The fact that this is the debt of your deceased mother, and if you were not a signer on the debt with your mother, then the question would be, why did the financial institution send you the document.
If the deceased received a 1099-C a year later, but there is no estate, then based on the individual facts and circumstances there may be no one responsible for filing a tax return with respect to the information tax documents addressed to the decedent. It is definitely not filed on a tax return for the decedent which was finalized in the year of death.
Assuming the Form 1099-C's tax year states 2017 and if she had an estate established, then the estate would be responsible for paying the tax on the income. In the absence of an estate, then you have nothing to report. You should consider reaching out to the financial institution for correction and/or a tax attorney depending on the amount of the debt.
